Preparing lithium ferrosilicon alloys



United States Patent 3,021,210 PREPARING LITHIUM FERROSILICON ALLOYS Joseph S. Mathias, Riverton, N.J., assignor to Foote Mineral Company, Berwyn, Pa., a corporation of Pennsylvania No Drawing. Filed May 26, 1960, Ser. No. 31,845 8 Claims. (Cl. 75-129) This invention relates to the production of homogeneous ternary alloys of lithium, and more particularly, provides novel methods for producing homogeneity and avoiding segregation in alloys of lithium with silicon and a third element.

Steel, and particularly stainless steel, is benefited by treatment with lithium, by virtue of the degassing effect of the lithium treatment, as Well as in other respects. However, lithium is diilicult to handle. It requires specialprecautions to keep it from oxidizing in storage. Its 'loW density makes it tend to float on the molten steel 'ra-ther than sink into the melt. Its relatively low boiling point produces substantial losses by volatilization during addition to the steel. Its reactivity with oxygen is also the cause of losses by combustion while it is being added to the hot steel.

For these reasons, it is preferred to add lithiumto steel in the form of a lithium alloy. A binary alloy like an alloy of lithium and silicon can be used for this purpose. Advantages would inhere, however, in the use of a ternary alloy of lithium, silicon and a third elementlike iron. Such a ternary alloy containing a heavy metal like iron would'be denser than the binary lithium silicon alloys, and have less activity than the latter.

The production of a homogeneous ternary alloy of this nature, however, has been found to present difiiculties not encountered in the manufacture of binary lithium alloys. When melts consisting of a combination of the components of the ternary alloy are allowed to cool and solidify, the alloy segregates instead of remaining a homogeneous mass. Segregation of the solidified alloy is objectionable. The industry requires that homogeneous alloys be supplied.

Methods which have been suggested hitherto for pre venting the segregation of alloys have various deficiencies. Thus for example, it has been suggested that alloy segregation be obviated by addin other metals to the alloy. This approach is unsatisfactory because the introduction of extraneous materials altering the composition of an alloywill usually also change its properties, and is therefore undesirable. Another method for inhibiting alloy segregation which has been suggested involves the application of centrifugal force to the alloy. Methods requiring special equipment like this are expensive to use. The industry requires methods which can be carried out in the equipment available and al- .ready in use in casting procedures.

An object of this invention i's-to provide novel methads for obtaining homogeneity :in castings of ternary alloys of lithium with silicon and a third element having an atomic number of .from 24 to 28.

A- particular objectof this invention is to prevent or minimize segregation of lithium ferrosilicon alloys in castings of such alloys.-

Another object is to provide an improved method for casting lithium ferrosilicon'.

Another object is to provide a novel method for producing lithium ferrosilicon alloys which tend to form homogeneous castings.

These and other objects will become evident from a consideration of the following specification and claims.

In accordance with this invention, segregation in castings of ternary alloys of lithium, silicon and a third element having an atomic number of from 24 to 28 is regation occurs.

reduced or eliminated by a metho'd comprising one or both of steps comprising, broadly stated, forming an alloy by combining lithium with an alloy consisting essentially of silicon and a heavy metal having an atomic number of from 24 to 28 in which the ratio of silicon to said heavy metal is substantially above about 5.0 weight percent, and casting a ternary alloy consisting essentially of lithium, silicon and a heavy metal having an atomic number of from 24 to 28 as a mixture of solid and liquid phases. I p I The stated first step is a novel method provided here'- by for forming a ternary lithium alloy tending to produce homogeneous castings. It has been found, in accordance with this invention, that castings substantially free of segregation can be formed, using known and usual methods of casting the alloy, when a ternary lithium alloy is formed by combining lithium in a melt with an alloy consisting essentially of silicon and a heavy metal having an atomic number of from 24 to 28 in which the ratio of silicon to heavy metal is substantially above about 50 weight percent. By contrast, when a silicon-heavy metal alloy containing less silicon than this is combined with lithium, the resulting melt, let stand to cool and solidify, forms an extremely inhomogeneous casting, which gives highly erratic results on analysis of different parts of the cast ingot. Thus the method of forming a ternary alloy of lithium, silicon and a heavy metal provided by this invention, in which the silicon-heavy metal ratio is controlled, is unexpectedly advantageous in preventing segregation.

Segregation is not, however, prevented in all cases. Under certain conditions, as set forth hereinafter, with conventional methods of casting these alloys, some seg- The above-stated second step of the invention is then usefully employed.

The stated second step is a novel method provided hereby for casting ternary alloys of lithium, silicon and a heavy metal having an atomic number of from 2 4 to 28 so as to prevent segregation. This is accomplished in accordance with this invention by casting such a ternary alloy as an intimate mixture of solid and liquid phases, in which from about 60% to about of 'the mixture is in the solid phase. The solid and liquidalloy phases can be produced by simply cooling a melt of the alloy unitl 60-90% of it has solidified. In the mill, for example, the alloy melt can be cooled'to separate it into phases in the same ladle in which the alloy components are combined to form the melt. It has been found that when the stated intimate mixture of solid and liquid phases of the alloy is cast, as for example by pouring such a mixture into a mold to set, the re sulting casting is homogeneous and free of segregation.

The present novel method of casting ternary lithium alloys of the above-stated composition, as will be evident from the foregoing descfiption, is very simple and direct. It requires neither special equipment nor the introduction of extraneous materials, and is thus advantageously superior to previously proposed methods of casting an alloy in such a manner as to avoid segregation. It produces castings which are greatly superior in homogeneity and freedom from segregation to castings of the same alloys-produced by methods of casting known hitherto.

It can beused to make homogeneous castings from a variety of ternary lithium alloys of the above-stated composition. These may be alloys produced by the novel method of this invention for forming such alloys, as

'hereinabove defined. As stated in discussing this method,

these alloys tend to form homogeneous castings. However, particularly at high lithiumcentents with'larg'e heats",

ingot geometry may sometimes cause these alloys tar-sag regate to a certain extent during casting. In such case,

3 the presently provided novel method of casting is advantageously used to cast ternary lithium alloys produced by the novel method of this invention for forming such alloys. Additionally, the presently provided novel method of casting so as to avid occurrence of segregation is also applicable to ternary lithium alloys made by combining the alloy components in a manner. different from the method of forming such alloys provided by this invention.

The desirable qualities of the products of the abovediscussed procedures for avoiding segregation provided by this invention will be immediately evident. By virtue of the fact that they are denser than binary lithium alloys like lithium-silicon alloys, and considerably denser than lithium itself, they are better adapted for the treatment of steel. They are also usually less reactive than lithium or binary lithium alloys, to an extent depending on their lithium content, and are therefore easier to store and handle. The homogeneity of these alloys is an important factor contributing to their usefulness. Quality control of steel melts makes it imperative to have accurate knowledge of the composition of additives to be used for treatment of .the melt. Whereas even multiple analyses of dilferent samples of a non-homogeneous ingot will not provide this information, analysis of only single samples of alloys produced in accordance with this invention, which are uniform and homogeneous in composition, gives true and representative figures for the composition of the ingots.

, The practice of the present invention as set forth in detail hereinbelow, may comprise either or both of the above-stated methods, that is, the method of combining the components of the alloy in which the composition of the alloy is controlled in respect to the ratio of silicon to .heavy metal, and the method of casting the alloy, in which a mixture of solid and liquid phases is cast into a mold. Considering first formation of the alloy in accordance with this invention, this comprises combining lithium with an alloy consisting essentially of silicon and a heavy metal having an atomic number of from 24 to 28, in which the proportion of silicon to said heavy metal is substantially above about 50 weight percent. The stated heavy metal will most usually be iron, which has an atomic number of 26. Alternatively, it may be one of the congeners of iron having an atomic number within the stated range. These heavy metals are manganese, chromium, cobalt and nickel. Of this group, at least manganese, chromium, and nickel are ordinarily present in steel of the stainless type, which isthe type for which treatment with lithium is usual. Accordingly, the ternary alloys produced have a composition such that the introduction of foreign, undesired elements into the steel melt is avoided.

, The proportion of silicon to the heavy metal in the ,binary silicon alloy used to'prepare the ternary lithium alloys must be substantially above about 50 weight per- ,cent. Generally, it must be at least about 55 weight percent. Among the ferrosilicon alloys, proportions of silicon ranging-from about 65 to about 85 weight percent have been found particularly suitable.

It will be desired to produce a ternary alloy containing at least enough heavy metal -to differentiate the ternary alloy from a binary lithium-silicon alloy, and preferably .enough' heavy metal to make the ternary alloy substantial- ;ly denser than a lithium-silicon alloy. Accordingly, the .silicon alloy employed herein will desirably contain at least about 5 weight percent of heavy metal.

The proportions in which the lithium is combined with the silicon alloy may vary over a broad range. There is ium ferrosilicon alloys are quite markedly active. Theoretical considerations, moreover, dictate an upper limit to increases of the lithium content substantially above this figure. It can be assumed that the liquidus temperature of the lithium-silicon phase in the alloy must be within a few hundred degrees (300 C., for example) of the melting point of the heavy metal-silicon phase to obtain inherently homogeneous alloys. For lithium ferrosilicon alloys, the melting point of FeSi being about 1400 C., an estimation of the liquidus of aloys ranging between Li Si and Si indicates that about 14 weight percent Li is the theoretical upper limit. For ternary alloys of lithium with silicon and others of the heavy metals which may be used herein, this theoretical limit will vary, depending on the melting point of the silicon-heavy metal alloys. Usually, however, to obtain alloys tending to remain homogeneous as they solidify, the lithium content will generally not be raised above about 15 weight percent.

In the discussion of the novel method of casting of this invention appearing hereinbelow, it is pointed out that the stated method may be used in casting ternary alloys containing up to 25 weight percent lithium. It is to be understood that the method of forming the alloy being discussed in the present section of this disclosure can be used to form such alloys containing in excess of the theoretical limit for the lithium content. A silicon-heavy metal binary alloy containing substantially above about 50 weight percent silicon, that is, may be combined with lithium in an amount suificient to produce an alloy containing above about 15 weight percent lithium. The product, unlike the ternary alloys containing less than about 15 weight percent lithium will not inherently tend to remain homogeneous and free of segregation upon being cast. However, such a procedure is within the scope of the invention insofar as the resulting alloy is cast by the novel method of casting of this invention. The stated method of casting will counteract and nullify tendencies to segregate during casting possessed by such ternary alloys of high lithium content. Therefore it is only insofar as this invention relates to forming ternary alloys tendin to solidify into homogeneous ingots when cast by conventional methods that the stated general maximum of 15 weight percent lithium applies.

Continuing now with description of the present novel method of forming ternary lithium alloys, the lithium can be combined with the silicon-heavy metal binary alloy by any convenient means whereby the components of the alloy are associated as a melt. Thus, the silicon alloy may be added, usually as a melt, to a melt of lithium. An alternative procedure, taking advantage of the fact that lithium is low melting, comprises combining solid lithium with a melt of the silicon alloy. The combining will usually be etfected in the ladle or other container in which the metal or alloy is melted, and the mixture subsequently poured into a mold to cool and harden. Substantially uniform alloy has been obtained, however, even where the lithium was added as a solid to the mold during the teeming operation, while the ferro-silicon alloy with which it was to be combined was being poured into the mold. To avoid too violent a reaction, it is usually desirable to combine the lithium with the binary silicon alloy gradually, in successive portions. Frequently the lithium sputters and burns while it is being combined with the silicon alloy and it is sometimes advantageous to protect the alloy by means of a flux cover. Any of the usual fluxes can be used for this purpose; generally, these will 'be inorganic fluorides like calcium or lithium fluoride.

However, after the lithium has been added, the molten alloy does not burn even without a flux cover. Thus, a suitable procedure consists in melting the silicon binary alloy under a flux cover, inserting lithium as a solid through the flux cover into the melt, and thereafter teeming the heat.

Ternary lithium alloys produced by the stated pro- 'perature at which the alloy is substantially molten.

Castings substantially free of segregation may be formed from such alloys using conventional metal casting procedures, consisting of letting the alloy stand, undisturbed, to cool in a mold from an initially totally molten state to an ultimate totally solid state. When the cast ingot has solidified, it will preferably be protected by being stored in sealed containers or sprayed with a mineral oil coating to prevent oxidation.

Coming now to the novel method of casting provided by this invention for producing castings free of segregation, this comprises casting a ternary alloy of lithium, silicon, and a third element having an atomic number of from 24 to 28 as a mixture of solid and liquid phases. More specifically, the method of this invention for casting to produce homogeneous ingots consists of reducing the temperature of an intimate mixture of solid and liquid phases of a melt of such a ternary alloy, in which from about 60% to about 90% of said mixture is in the solid phase, to a temperature at which said alloy is totally solidified. The stated mixture of solid and liquid alloy phases is produced, as further described hereinafter, by cooling a melt of the alloy until 6090% of the melt has solidified.

The usual method of casting an alloy, as will be known to those skilled in the art, consists of pouring a totally molten melt of the alloy into a mold, and letting it stand and cool undisturbed in the mold until it solidifies. In contrast to this, in acordance with the method of this invention, it will be a mixture of solid and liquid phases which is let stand and cool in the mold until it solidifies, instead of a melt.

A preferred embodiment of this method is a process wherein the ternary lithium alloy is converted from an initial wholly molten state to a final wholly solid state, comprising the steps of first providing the mixture of solid and liquid phases of the alloy and then casting this mixture to produce a homogeneous casting. This embodiment of the invention, briefly stated, starts with a homogeneous melt of the ternary lithium alloy at a tem- The first step of the process consists in reducing the temperature of this melt to a lower temperature at which from about 60% to about 90% of the melt has solidified, and the melt comprises a solid phase and a liquid phase. Preferably, the melt is held quiescent while it is cooled, in which case the stated procedure forms a stratified product, in which the lower layer is solid and the upper layer is liquid. The solid and liquid alloy phases will be mixed, to produce an intimate mixture of the solid phase with the liquid. The last step then consists in reducing the temperature of this intimate mixture of solid and liquid alloy phases to a temperature at which the alloy is entirely solidified, thus forming a homogeneous casting of the alloy.

The stated process comprising the step described above is a particularly advantageous embodiment of the invention. It takes the alloy from the point when it has first made, by mixing its components, and carries it through to the point where the alloy is in its ultimate, saleable form of a homogeneous casting. The preferred practice of the casting method of this invention will generally consist of the stated process, including forming the solidliquid phase mixture and then casting it. It accordingly will be described hereinafter with particular reference to this embodiment thereof.

Referring to the alloys to which this method of casting is applicable, these are ternary alloys of lithium, silicon and a third element, said third element being a heavy metal having an atomic number of from 24 to 28. The said third element may be iron or a congener of iron selected from chromium, manganese, cobalt and nickel. Lithium ferrosilicon alloys are the species in connection with which the stated method is particularly useful.

The ternary alloys to which this method of casting is applied may be prepared by the novel method described hereinabove, comprising combining lithium with an alloy consisting essentially of silicon and a heavy metal having an atomic number of from 24 to 28 in which the ratio of silicon to heavy metal is substantially above about 50 weight percent. As hereinabove stated, when this method is used to form the ternary alloys, they tend to form homogeneous castings. However, under certain conditions they may exhibit segregation of a type which appears to be connected with the nature of the alloy structure. Metallographic study of such castings of lithium ferrosilicon alloys which are free of segregation and homogeneous on a macroscopic scale indicates that the cast alloys actually consist of two phases: a matrix of ferrosilicon, and homogeneously distributed through this matrix, a phase consisting of silicon containing lithium in solid solution. An area count of the photomicrograph of the metallographic specimen and chemical analysis of the specimen are in close agreement with the assumption that all the silicon tied up with the iron is present as FeSi. The two different types of metallic phases present differ in density and melting point. This difference is particularly accentuated when the lithium content of the alloy is high.

When the alloys are being handled in large scale heats, the ingots poured are large and therefore the rate of cooling of the alloy is slow. Under these circumstances, particularly when the lithium content of the ternary alloys is high, segregation then sometimes occurs in the mold. This segregation is of such a type that the ingot has a substantially higher lithium content in its interior than in the outside section. It appears that the occurrence of this type of segregation is connected with the presence in the alloy of the low density, low melting point, lithium-rich phase and high density, high melting point ferrosilicon phase detected in the metallographic studies described above. With substantial differences between these properties of the respective phases and with a slow cooling rate permitting the effects of these properties to be exerted to a substantial degree, an initially homogeneous distribution of the phases is converted into an uneven distribution, so that the resulting casting exhibits segregation.

The casting method of this invention is particularly applicable to the solution of the problem presented by this situation. In general, the ternary alloys treated will then comprise at least about 5 weight percent lithium, and frequently will contain up to about 10 weight percent lithium. With this technique of casting, the proportion of lithium in the ternary alloy may be substantially increased as compared to the lithium content which can be used otherwise, without the appearance of segregation in the cast ingot. Thus, the lithium content may exceed 15 weight percent, and indeed, may be as high as about 25 weight percent or even higher.

It is to be appreciated that additionally, the method of this invention may also be applied, if desired, to ternary lithium alloys prepared by methods other than that provided by the present invention. In such case, the alloys treated may not have the inherent tendency to homogeneity of those prepared by the method of this invention, and the segregation thereof may have its causes in factors other than ingot geometry. They will contain the components present in the above-discussed ternary alloy: lithium, silicon, and a heavy metal having an atomic number of from 24 to 28; but the proportions of these components one to another may vary from those in the homogeneous alloys which will be produced by the preparative method of this invention.

In conducting the casting procedure in the embodiment thereof comprising a multi-step process, the temperature of the alloy at the beginning of the first step of the process will be such that the lithium/heavy metal/silicon mixture is substantially entirely molten. While the molten ternary alloy may be ternary alloy previously prepared and solidified, and later melted, usually the present process will most conveniently be applied commercially immediately following after preparation of the alloy, While the alloy is still molten. Thus, for example, the alloy may be prepared in molten form by combining molten ferrosilicon with lithium metal. Generally, the alloy melt will conveniently be prepared in the ladle used in casting operations for introducing metals into molds. The temperature of the molten ferrosilicon and of the lithium/iron/ silicon melt resulting from its combination with the lithium may, for example, be from 2600 to about 2900 F.

The alloy melt at this point, when it is an initial temperture such that it is substantially entirely molten, should be homogeneous in composition. A melt produced, for example, by charging ferrosilicon into a ladle containing lithium melt may be stirred to achieve homogeneity of the melt composition.

The first step of the casting process consists of reducing the temperature of the homogeneous melt of lithium, heavy metal and silicon from a temperature at which it is substantially entirely molten to a temperature at which from about 60% to about 90% of the melt has solidified. Conveniently the temperature of the melt will be reduced by simply holding it in the ladle, under conditions permitting the heat of the melt to escape. During this period, the melt will preferably remain quiescent. As the temperature of the melt decreases, a gradual crystallization and solidification of a portion of the melt occurs, and this portion of the melt which crystallizes out will settle to the bottom of the ladle or other container in which the quiescent melt is held.

The reduction of the temperature of the melt will be continued until a major portion, but less than all of the melt has solidified. Generally, the portion of the melt permitted to solidify will advantageously constitute about three-quarters (75%) by volume of the total volume of the melt. However, the exact proportion of the melt which is permitted to solidify is not critical, and the volume of the melt solidified may deviate from this figure. It may, for example, vary over the range of from about 70% to about 80%. Variation over an even wider range, from about 60% to about 90%, may sometimes be permissible, depending on the total volume of the melt, the rate of cooling of the melt and similar factors.

The temperature of the melt at this stage, when it has been partially solidified as described, will be from about 1400 to about 1600 F., for the lithium ferrosilicon alloys constituting the preferred species for treatment as herein described.

In accordance with the present novel process, the portion of the melt which has been solidified must be mixed with the portion of the melt which remains liquid, to produce a solid-liquid mixture. The solid and liquid portions of the melt should be well mixed together, to produce an intimate blend of the solid and the liquid phases. In small scale operations, the phases can be mixed by stirring with a metal rod, for example. For larger production batches, a rocking furnace may be used to effect the mechanical mixing of the crystals and the liquid melt. The intermingling of the solid and the liquid portions of the partially solidified melt will result in the formation of a mixture having the consistency of a mush.

If the melt is quiescent during the period While the temperature of the alloy melt is reduced to produce a gradual partial solidification of a solid portion from the melt, as described above, a stratified composite of solid and liquid phases, with the solid phase forming the lower layer, will be produced. Generally, it will be convnient to stir up the stratified composite of solid and liquid phases formed while setting forth an especially" advantageous mode of providing the mixture of solid and liquid phases of alloy used to prepare 'a casting in accordance with the novel method of this invention, is not necessarily limiting. For

example, instead of letting the melt stand to cool and then stirring it, the melt may be stirred While it is cooling and partially solidifying, as for example by bubbling an inert gas through it. if a mold of the necessary strength were used, the alloy could be poured in the molten state into the mold, let stand until a major part of the melt had solidified, and then the liquid and solid phases present could be stirred together to provide an intimate mixture of solid and liquid phases Within the mold.

Where, however, the solid-liquid phase mixture is formed in a container other than the mold, as will normally be the case, the alloy will be cast by pouring the intermixture of solid and liquid phases into a mold where the temperature of the intimate solid-liquid mixture is re duced to a temperature at which the entire alloy is solidified. Ordinarily, the latter will be the ambient temperature of the area, and the temperature reduction will be effected simply by letting the alloy lose heat to its surroundings until it reaches room temperature. During this decrease in temperature, the alloy will be held in the container in which it has been cast, which will suitably be a mold such as a pig mold. The casting of the alloy produced by this method, in which the intimate mixture of solid and liquid phases is entirely solidified, will be a homogeneous casting in which segregation is reduced or substantially eliminated as compared to the segregation occurring in castings of the same alloy prepared bycooling directly from the liquid melt to the solid casting, without intermixing phases of the alloy as herein described.

The invention will be better understood by a consideration of the following illustrative but not limiting examples.

Example I This example illustrates the operation of the method of this invention for the preparation of the ternary lithium alloy.

Five pounds of 65% ferrosilicon (an alloy of 65% by Weight silicon, balance iron) were melted in the electric furnace and g. of lithium were added in 25 g. chunks to the molten ferro alloy. The lithium chunks were speared on the end of a steel rod and the rod quickly plunged into the molten ferro alloy. There was some sputtering and burning. The molten material was poured into the ingot mold. On cooling, 2. very uniform ingot was obtained. Analysis of the material was as follows:

2.88% Li; 64.93% Si; balance Fe.

Example 11 The procedure described in Example I was repeated. Again a uniform ingot was obtained. Analysis of the ma- 'terial indicated that it contained 3.2% Li (73% Li recovery) Example III This example illustrates the essentiality of observing the conditions of the method of this invention if homogeneous alloys are to be obtained.

The procedure described above in Example III was followed but substituting 5 pounds of 50% ferrosilicon (a 1:1 by weight alloy of silicon and iron) for the 5 pounds of 65 ferrosilicon used in Example 111. The

ferrosilicon was melted in the electricfurnace and 12 g. of lithium were added in chunk-s to the mold While the molten ferro alloy was being poured. The reaction was fairly vigorous and there was some burning. The alloy on. cooling was very inhomogeneous and gave highly erratic results on analysis from different parts of the cooled ingot.

The same lack of success in producing a homogeneous alloy was experienced 'in're'peated experiments in which lithium was added to molten 50 ferrosilicon.

Example V This example illustrates operation of the preparative method of this invention to obtain a ternary alloy of high lithium content.

Five pounds of 65% ferrosilicon were melted in the electric arc furnace and 300 g. of Li metal were added in 25 g. chunks. There was some sputtering. The molten metal was poured into the ingot mold and, on cooling, appeared to be uniform. The analysis of the material was as follows: 12.93% Li; 61.49% Si; balance Fe.

Example VI This example illustrates operation of the preparative method of this invention using a high silicon binary alloy.

Five pounds of 85% ferrosilicon (an alloy containing 85% by weight silicon, balance iron) were melted in the electric arc furnace and 125 g. of Li metal were added in 25 g. chunks using the same technique as in Example I. There was some sputtering. The molten metal was poured into the ingot mold. On cooling, a uniform ingot was obtained. Analysis of the material was as follows: 5.07% Li; 67.54% Si; balance Fe.

Example VII This example illustrates use of a flux in the preparation of a homogeneous ternary alloy.

Seven and one-quarter pounds of 65% ferrosilicon were melted in the arc furnace. When all the ferrosilicon had melted, 350 g. of fluorspar were added to act as a flux cover. 235 g. of lithium were added in 75 g chunks by spearing and immersion into the molten metal, The reaction was fairly vigorous with some sputtering and burning. The melt was poured into ingot molds and showed a nice grey apparently uniform structure. The analysis of the material was as follows: 3.84% Li; 63.45% Si; balance Fe.

Example VIII This example illustrates operation of the casting method of this invention for preventing segregation of the ternary alloys in the mold.

An alloy consisting of %lithium, 25-28% iron and 62-65% silicon was prepared by adding nine parts by weight of molten ferrosilicon at a temperature of 2600- 2900 F. to one part of lithium metal held in a ladle. The molten alloy was well stirred, and then allowed to stand in the ladle while its heat was lost to a surrounding environment of air at room temperature. When the temperature of the melt had dropped to 1400-16-O0 F., about 75% by volume of the ladle contents had crystallized out from the melt and settled to the bottom of the ladle. The supernatant liquid phase was then well stirred into the crystallized phase, and the resulting mixture of mush-like consistency poured into pig molds. When the contents of the molds had cooled to room temperature, to produce solid casts of the alloy, the casts were removed and subjected to examination and analysis. It was found that the alloy casts were free of segregation and homogeneous in composition: analysis gives a figure of 9.79% Li for a section taken from the center of a cast, and 9.90% Li for an outside section.

By contrast, segregation is pronounced in a cast of a lithium ferrosilicon alloy of high lithium content made by adding molten ferrosilicon to lithium metal in a ladle,

mixing well, and then immediately pouring the molten alloy into a pig mold to solidify. Using this procedure and em loying an amount of lithium metal calculated to give a 14.1% lithium content in the alloy, analysis of the cast gave a value of 12.99% Li for the center section, and only 10.67% Li for an. outside section. It will accordingly be evident "that the method of this invention produces a casting of lithium ferrosilicon alloy which is very much superior in homogeneity of composition to castings produced when treatment by the presently pro vided method is omitted.

While the invention has been described with particular reference to individual preferred embodiments thereof, it is to be appreciated that modifications and variations can be made Within the scope of the foregoing description and appended claims:

What is claimed is:

l. The process of preparing a homogeneous casting of a lithium ferrosilicon alloy which comprises (1) reducing the temperature of a substantially homogeneous lithium ferrosilicon alloy melt, from an initial temperature at which said melt is substantially completely molten, to a lower temperature at which from about 60% to about 90% of said melt has solidified into a solid alloy phase; (2) intimately mixing said solid alloy phase with the liquid alloy phase comprising the remainder of said melt to form an intimate mixture of solid and liquid alloy phases; and (3) reducing the temperature of said intimate mixture of solid and liquid alloy phases to a temperature at which said alloy is entirelv solidified.

2. The process of claim 1 in which said melt is substantially quiescent during the reduction of the temperature of said melt; the temperature of said melt is reduced from an initial temperature of about 2600-2900" F. to a lower temperature of about 1400-1600 F.; and from about 70% to about of said melt settles out as a solid phase from said melt during the reduction of the temperature of said melt.

3. The process of claim 1 in which said lithium ferrosilicon alloy melt is prepared by combining lithium with a ferro-silicon alloy in which the ratio of silicon to iron is substantially above about 50 weight percent.

4. The process of claim 1 in which said lithium ferrosilicon alloy melt is prepared by combining lithium with a ferro-silicon alloy in which the ratio of silicon to iron is at least about 65 weight percent.

5. The process of preparing a homogeneous casting of a lithium ferrosilicon alloy which comprises reducing the temperature of a substantially quiescent, homogeneous, completely molten lithium ferrosilicon alloy melt from an initial temperature of about 2600-2900 F. (until about 75% of said melt has settled out from said melt as a solid alloy phase at a lower temperature of about 1400-l600 F.; mixing said solid alloy phase with the liquid phase comprising the remainder of said melt to produce an intimate mixture of solid and liquid alloy phases; and transferring said intimate mixture into a mold in which the temperature of said mixture is reduced to a temperature at which said alloy is entirely solidified.

6. The process of preparing a casting of a lithium ferrosilcon alloy substantially free of segregation which comprises combining lithium with a ferrosilicon alloy containing at least about 55 weight percent silicon to provide a melt of a lithium ferrosilicon alloy containing at least about 5%, by weight, lithium; reducing the temperature of said melt until from about 70% to about 80% of said melt has solidified into a solid alloy phase; intimately mixing said solid alloy phase with the liquid alloy phase comprising the remainder of said melt to form an intimate mixture of solid and liquid alloy phases; and reducing the temperature of said intimate mixture of solid and the liquid alloy phases to a temperature at which said alloy is entirely solidified.

7. The process of claim 6 in which said lithium ferrosilicon alloy contains up to about 25%, by weight, lithmm.

8. The method of reducing and eliminating segregation in the mold during casting of a tertiary lithium alloy which comprises reducing the temperature of a mixture of a solid phase and a liquid phase, in which from about 60% to about 90% of said mixture is said solid phase, of a melt of an alloy consisting essentially of lithium, silicon and iron, prepared by combining lithium with a ferrosilicon alloy in which the ratio of silicon to iron is substantially above about 50 weight percent, to a term perature at which said mixture of solid and liquid phases is entirely solidified.

References Cited in the file of this patent FOREIGN PATENTS 145,172 Austria Apr. 10, 1936 

1. THE PROCESS OF PREPARING A HOMOGENOUS CASTING OF A LITHIUM FERROSILICON ALLOY WHICH COMPRISES (1) REDUCING THE TEMPERATURE OF A SUBSTANTIALLY HOMOGENOUS LITHIUM FERROSILICON ALLOY MELT, FROM AN INITIAL TEMPERATURE AT WHICH SAID METLT IS SUBSTANTIALLY COMPLETELY MOLTEN, AT A LOWER TEMPERATURE AT WHICH FROM ABOUT 60% TO ABOUT 90% OF SAID MELT HAS SOLIDIFIED INTO A SOLID ALLOY PHASE; (2) INTIMATELY MIXING SAID SOLID AND LIQUID THE LIQUID ALLOY PHASE COMPRISING THE REMAINDER OF SAID MELT TO FORM AN INTIMATE MIXTURE OF SOLID AND LIQUID ALLOY PHASES; AND (3) REDUCING THE TEMPERATURE OF SAID INTIMATE MIXTURE OF SOLID AND LIQUID ALLOY PHASES TO A TEMPERATURE AT WHICH SAID ALLOY IS ENTIRELY SOLIDIFIED. 